Question

The following reaction depicts the activity of a particular class of enzymes :

X    Y
|    |
C - C → X - Y + C = C

(Substrate)      (Product)    (Product)

Identify the enzyme class 'E' from the following options :

• A. Ligases
• B. Transferases
• C. Lyases
• D. Isomerases

Hint:

Logic Tip: The key visual cue for a Lyase reaction is the formation of a double bond upon the removal of groups. No water involved (not a hydrolase) + double bond created = Lyase.

Answer 1

The Correct Option is C

Step 1 : Understanding the Question:
We are given a generalized chemical equation showing a transformation of a substrate into two products. The goal is to identify which of the six IUBMB classes of enzymes catalyzes this specific type of reaction.
Step 2 : Key Formulas and Approach:
We analyze the chemical changes occurring from substrate to product:
1. Observe if groups are being removed or added.
2. Check for the formation of double bonds.
3. Determine if water is involved (hydrolysis).
4. Evaluate the options based on standard enzyme classification definitions.
Step 3 : Detailed Explanation:

Analysis of the Reaction: The substrate contains two carbon atoms ($C-C$) linked by a single bond, with groups X and Y attached to them. In the product phase, the X-Y molecule has been removed, and a double bond ($C=C$) has been created between the carbons.

Defining Lyases: Lyases are enzymes that catalyze the removal of groups from substrates by mechanisms other than hydrolysis, typically leaving double bonds behind. They can also catalyze the addition of groups to double bonds. The reaction provided is the classic representation of a Lyase.

Excluding Other Classes:
Ligases (A): Catalyze the joining of two molecules using ATP (not seen here).

Transferases (B): Catalyze the transfer of a group from one molecule to another (not seen here).

Isomerases (D): Catalyze structural rearrangements within a single molecule (not seen here).


Step 4 : Final Answer:
The formation of a double bond through the removal of groups without the addition of water is the hallmark of the class Lyases. Therefore, the third option is the correct identification.